1. Field of the invention
The present invention relates to apparatus and methods for manufacturing digitized video systems and integrated circuits and devices therefor.
2. Description of the Prior Art
The present invention is useful in the field of graphics and video display systems such as displays for computer systems, terminals and televisions. Recently there has occurred a large demand for larger and/or higher resolution viewing surfaces than can be provided by conventional video display devices such as cathode ray tubes (CRTs) or liquid crystal displays (LCDs). This has been driven by consumer demands for larger televisions (TVs) and by the need for large audience viewing of either shows or computer generated screens in conferences.
LCDs, which are used for small computer systems and terminals, especially for laptop and portable computers, use individual liquid crystal cells for each pixel on the LCD. LCDs are temperature sensitive, difficult to produce in large sizes, slow in changing state, and require external light sources for viewing.
To overcome the size limitation of LCDs, there have been attempts to construct projection systems using an LCD as a spatial light modulator (SLM). Unfortunately, several problems still remain. The LCD is inherently slow and thus a rapidly changing image will "smear." The resolution of the LCD is restricted by the drive complexity. Further, the drive complexity also requires that the size of the LCD will generally be proportionally related to the resolution. This means that the projection optics will have to be large and correspondingly expensive for a high-resolution system. Another problem is that the light transmitted through (or reflected from) the LCD will be polarized. This may result in non-linear perception of brightness from the center of vision to the periphery.
The most popular display system is the CRT. In a cathode ray tube, a scanning electron beam having a varying current density, is scanned across a light emitting phosphor screen. This light emitting phosphor screen is bombarded by the electron beam and produces light in relation to the magnitude of the current density of the electron beam. These may also be used in a direct view or projection mode. However, these suffer from various disadvantages. The first of these is cost.
The higher cost is dictated by the difficulties in constructing large display tubes (at present there are 45 inch tubes being manufactured). Another reason for the cost is the huge amount of raw materials (in particular the glass) required. This translates to a very heavy display that is not easily transportable.
Resolution is also a problem for CRTs. There are two major reasons for this. The first relates to the shadow mask used in color CRTs. A shadow mask is used to separate the color phosphors used to generate the three primary colors (red, blue, and green), and to help guide the electron beam used to excite the phosphors. The brightness of a pixel is related to the size of the phosphor spot. However, as the phosphor spot size is increased, the shadow mask must be made larger and becomes more visible. Brightness is also related to the drive from the electron beam. As the drive increases, so does the brightness. Unfortunately, the shadow mask is also sensitive to the electron beam and will thermally distort under high drive. The image is then blurred both by the shadow mask becoming more visible and by the electron beam being deflected toward an unwanted phosphor.
The second resolution limiter is rastering. All pixels to be illuminated are sequentially scanned by an electron beam. This beam is swept in a raster back and forth across the phosphors. In general, the beam is turned off when tracing back across the phosphors (known as the retrace time) and is also turned off when returning to the starting point (vertical blanking interval). While this is not a theoretical limitation (all phosphor points can be accessed), it is a practical limitation. This is because the fluorescence of the phosphors begin decaying as soon as the electron beam moves to the next location. The electron beam must return before the human eye can perceive the decay or else the display will flicker. Longer persistence phosphors can be used to compensate, but they suffer from a smear effect when the display data changes.
Rastering has another insidious side-effect. It places an upper limit on the perceived brightness of a display. As discussed above, a phosphor can only be driven for a very short period of time, and will then start to decay. If the phosphor is driven hard, then it will start to bloom (i.e. it will start to excite neighboring pixel locations) and blur the display. If the phosphor was continuously excited for an extended time, it would appear to be brighter than if it was excited only for the raster period. This is because the human eye has an integration time of approximately 0.1 seconds for bright sources of light and approximately 0.2 seconds for dimmer sources.
Projection CRT based systems do not suffer from the shadow mask problems. However they are expensive as they usually require three CRTs (one each of red, blue, and green). Also, they suffer badly from low brightness (due to having expand the image generated). This is particularly true when a single CRT is used in a projection mode. Either type has all of the other raster related problems. In addition, when used in back-projection configurations, they are very large due to the complex optical paths required.
Another drawback to conventional display systems is that they are primarily analog. Even if the information to be displayed is stored in digital form as in a computer, it must be converted to an analog raster scan before it can be displayed on the cathode ray tube.
Other spatial light modulators have been used in projection displays. For example, the use of a spatial light modulator drive for in a display system is shown in U.S. Pat. Nos. 4,638,309 and 4,680,579 issued to Ott and incorporated by reference hereinto. In Ott, a semiconductor deformable mirror device, in conjunction with a Schlieren optical device, is used to form the spatial light modulator. Deformable mirror devices are shown in U.S. Pat. Nos. 4,441,791, 4,710,732, 4,596,992, 4,615,595, and 4,662,746, and U.S. patent application Ser. No. 168,724, filed Mar. 16, 1988 by Hornbeck, all of which are incorporated by reference hereinto.
Another display utilizing a light valve is shown in U.S. Pat. No. 3,576,394 by Lee, which is incorporated by reference hereinto. Various types of human factors information on critical flicker frequency is shown in "Applied Optics and Optical Engineering" (1965), Volume II (The Detection of Light and Infrared Radiation), by Rudolf Kingslake, which is incorporated by reference hereinto. Acousto-optic spectral filters are shown in I.E.E.E. Transactions on Sonics and Utrasonics, vol. su-23, No. 1, January 1976, pages 2-22, which is incorporated by reference hereinto.
A HDTV (High Density TeleVision) system is shown in U.S. Pat. No. 4,168,509 by Hartman, which is incorporated by reference hereinto. Various types of electronic TV tuners are shown in U.S. Pat. Nos. 3,918,002, 3,968,440, 4,031,474, 4,093,921, and 4,093,922, which are incorporated by reference hereinto. Various multi-frequency sensitive materials for displays are shown in SPIE vol. 120 (Three-Dimensional Imaging, 1977), pages 62-67, "PRESENT AND POTENTIAL CAPABILITIES OF THREE-DIMENSIONAL DISPLAYS USING SEQUENTIAL EXCITATION OF FLUORESCENCE" by Carl M. Verber; and IEEE Transactions on Electron Devices, Vol. ED.-18, No. 9 September 1971), pages 724-732, "A True Three-Dimensional Display" by Jordan D. Lewis et al, which are incorporated by reference hereinto. A type of Display is shown in Information Display, November/December, 1965, pages 10-20, "Three Dimensional Display Its Cues and Techniques" by Petro Vlahos, which is incorporated by reference hereinto.
Laser (Light Amplification by Stimulated Emission of Radiation) based projection systems are well known in the art. These systems may also use fluorescing pigments with non-visible laser light. This is shown in SID INT. SYMP. DIGEST, Paper 10.1, May 1983, "Projection Display of Radar Image using Gas Laser and Organic Fluorescent Pigment Screen" by H. Yamada, M. Ishida, M. Ito, Y. Hagino and K. Miyaji, which is herein incorporated by reference. More details on various pigments may be found in CHEMISTRY AND CHEMICAL INDUSTRY, Vol. 23, No. 3, 1970, "Increasing Application Field for Fluorescent Pigment" by R. Takano, which is herein incorporated by reference.
Laser based displays operate by deflecting a beam of coherent light generated by a laser so as to form an image. The deflectors include devices such as spinning mirrors and acousto-modulated deflectors. There are a number of problems with these projectors that have prevented them from becoming commercially feasible.
The first of these problems is flicker, which also places an upper limit on the resolution (i.e. number of pixels displayable) obtainable. Only one point of light (pixel) can be displayed at any given moment due to the nature of the deflectors. Also, there is no persistence to the display as these projectors generally direct the light onto a diffusion surface which have no means of continuing to emit light after the light is deflected away. This means that all points to be displayed must be illuminated within a time period less than the critical flicker frequency (CFF) of the human eye.
A second problem is laser speckle. This is considered to be a random interference pattern of intensity which results from the reflection of transmission of highly coherent light from (or through) an optically rough surface (one whose local irregularities in depth are greater than one quarter of a wavelength). This phenomenon is dealt with in JOURNAL OF THE OPTICAL SOCIETY OF AMERICA, Vol. 66(11), 1976, page 1316, "Topical issue on laser speckle" by N. George and D. C. Sinclair; APPLICATIONS OF OPTICAL COHERENCE (W. H. Carter, Ed.), 1979, pages 86-94, "Role of coherence concepts in the study of speckle" by J. W. Goodman; and COHERENT OPTICAL ENGINEERING (F. T. Arecchi and V. Degiorgio, Eds.), 1977, pages 129-149, "Speckle interferometry" by A. E. Ennos, all of which are incorporated herein by reference. Techniques for reduction of speckle are also shown in JOURNAL OF THE OPTICAL SOCIETY OF AMERICA; PART A, Vol. 5(10), 1988, pages 1767-1771, "Effect of luminance on photoptic visual acuity in the presence of laser speckle" by J. M. Artigas and A. Felipe and OPTICS COMMUNICATIONS, Vol. 3(1), 1971, "Elimination of granulation in laser beam projections by means of moving diffusers" by E, Schroder, all of which are incorporated herein by reference.
Another problem has been the generation of color images. This requires the use of multi-colored lasers. There are great technical difficulties in both aligning multiple deflectors and in keeping them synchronized so as to simultaneously image the different colors at a given pixel location.
As shown in the above articles and Patents there have been attempts to implement three dimensional displays. None of these constructions provides a practical true three dimensional display. Further, as shown in the above articles there have been attempts to implement two dimensional displays using light valves, lasers, and deformable mirror devices. None of these constructions provides a two dimensional display which is adaptable to many different TV and computer display formats and provides a fully digitized video display system using deformable mirror devices.